Wednesday, September 24, 2014

I had a problem with MSCS cluster when I rebooted one of the ESXi host & found that ESXi host was stopped responding at the time of boot / discovery.

Then I got to know that there were 32 RDM were mapped to VM which were causing the issue

What are perennial reservations and why are they needed? Whenever a LUN is participating in a MSCS cluster, the active node has ownership of that device(s) using permanent SCSI reservations. Now, whenever you rescan for devices on an ESXi host, or are booting an ESXi host, the host tries to query all devices that it can see, including the devices used for MSCS. Now, I'm not exactly sure what takes place during the query process, but because the MSCS device(s) are already have a permanent SCSI reservation, the ESXi query to the device fails, and will continue to fail until the host decides to move on

To solve the problem of of ESXi trying to query MSCS owned devices, a flag has been introduced on a device calledIs Perennially Reserved. By default this flag is set tofalse. By setting this flag to trueit lets the ESXi host know to essentially, NOT query this device during rescans/boot time. Here'sVMware KB 1016106that describes that problem/resolution